Our concentric diffusers are manufactured with all aluminum construction and have a completely sealed and insulated box. In addition, our unique design – which includes the industry’s only molded transition for 2-5 ton models and a “supply-through-return” duct installed on the larger models – delivers maximum airflow to all four sides of the diffuser. Because we take these steps in the design and manufacturing process the RRS line of diffusers consistently delivers more air to the conditioned space than any concentric diffuser on the market.